CA1139249A - Two-stage coaxial spring damper - Google Patents

Abstract

Title TWO-STAGE COAXIAL SPRING DAMPER

ABSTRACT OF THE DISCLOSURE
A clutch driven disc assembly is disclosed having coaxial damper springs between rotary elements of the disc assembly. Each element has spring receiving openings with the end walls which permit the springs to operate in two stages, thereby varying the deflection rate between the rotary elements.

Description

~L139249 Title T~O-STAGE COAXIAL SPRING DA~PER
B kground of the Invention This invention relates to rotzry torque transmitting devices in general and is particularly directed to an improved dzm?er arrangement for these devices.
In conventional passenger cars and trucks, objectionable driveline vibrations may occur at certain speeds and load conditions. Some of these disturbances may be eliminated or reduced to an acceptable level with the incorporation of a torsional damper in the driven disc portion of the vehicle clutch. Damping is normally provided by 2 plurality of circumferentially spaced coiled springs operatively connected between relatively rotatable elements of the clutch driven disc assembly.
Clutches with dampers are widely use~ in all types of : power transmissions systems. In certain applications, it has been found advantageous to have a damper arrangement ~hich permits varying rates of deflection between the rotary elements.
The purpose of this type of arrangement is to have a damper function in a first torsional range to produce a low àeflection rate for overcoming minor vibrations, chatter and the like, and in a succeeding torsional range to produce a high àeflection rate for accommodating peak shock loads and for high torque load transmission.
Rnown devices have achieved two-stage dampinc by providing heavy and light springs which act in series and by coaxially arranging springs which operate in parallel. In the first instance, it is necessary to reconstruct the spring 3~ openings of conventional rotary elements to accommodate the added length of a second spring or to reduce the axial length of both springs in order.to fit conventional openings.
To function properly, the latter coaxial spr-ng design has required either considerable struc~ural modifications in the mating spring openings of the relatively rotatable elements or, when conventional openings are used, springs of differino lengths. ~either is entirely satis~actory from a structural or cost standpoint.

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11392~9 Thus, while the two-stage concept is not new, the known methods used to accomplish the desired results are not acceptable in heavy duty applications for one reason or another.
It is an object of the present invention to provide a clutch driven disc with an improved two-stage coaxial damper spring arrangement which is simple in design and will not require any additional space to accomplish the desired result.
Summary of the Invention The above and other objects are preferably achieved in the present invention by providing modified spring openings in one of the relatively rotatable elements of the clutch.
'rhese openings permit the inner springs to operate at light loads and both springs to operate at higher or maximum load conditions.
In accordance with the present invention there is provided a torque transmitting device comprising a hub, a cover secured to said hub, said cover defining at least one opening having spaced side walls, a plate mounted on said hub for limited rotation relative to said hub and said cover, said plate defining at least one opening having spaced side walls, said plate opening adapted for alignment with said cover opening, resilient means disposed in said aligned openings adapted to transmit a yieldable drive between said hub and said plate, said resilient means comprising a first resilient member and a second resilient member disposed in said first resilient member, each of said resilient members having end portions, means on at least one of said plate or cover opening side walls for engaging one of said resilient members, at least one end portion of one of said resilient members spaced from said plate or cover opening side wall engaging means and engageable there-with upon limited relative rotation between said plate and said cover, and at least one end portion of the other of said ~1392~9 resilient members engaging said plate or cover opening side wall engaging means.
Brief Descri~etion of the Drawings Figure 1 is a partially broken away end elevational view of a clutch driven disc assembly incorporating the principles of the present invention;
Figure 2 is a sectional view taken along lines 2-2 of Fig. l;
Fig. 3 is a partial end elevational view of one of the covers shown in Fig. l;
Figure 4 is a partial end elevational view of one of the friction pad support plates shown in Fig. l;
Figure 5 is an enlarged fragmentary section view taken substantially along line 5-5 of Fig. 1 to more clearly show the resilient drive means and associate parts;
Figure 6 is an enlarged fragmentary section view taken along line 6-6 of Fig. 1 with the resilient drive means removed;
Figure 7 is a partial end elevational view taken substantially along line 7-7 of Fig. 2 showing the position of parts in their inactive state;
Figure 8 is a view similar to Fig. 7 showing the first stage of operation;
Figure 9 is an enlarged section view taken along lines 9-9 of Fig. 8; and Figure 10 is a graph illustrating a typical torque input versus angular deflection curve for the various types of disc applications.

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1139~49 Description of a Preferrec rrbociment Referring to Figs. 1 and 2 of the drawinys, in 2 prelerred embodiment, the rotary torque trans~itting device is a dampened arive disc assembly shown a. 10. In normal practice, 5 the disc assembly 10 is the driven portion of a clutch which is positioned in a vehicle power line between an engine and a transmission (not shown). The disc assembly 10 comprises rotary torc~e transmitting elements connected by a damper uni~ cesigned to es.ablish a resilient drive between the rotary elements. The 10 damper unit is needed to tune the vehicle arive train ~ystem so that critical torsional vibrations are ~oved out of the operating speed range of the e~gine and drive train.
In the preferred embodiment, one rotary torque transmitting element of the disc assembly 10 includes G roiatably 15 hub 12 ana a pair of spaced outer annular covers 14. ~n integral rad~al extending annular flange 16 is formed on the hub 12 with the covers 14 arranged on opposite sides of the flange 16.
The outer rotary element of the disc assembly 10 includes a rotatable disc or support plate 18 having ir,tegral 20 radially outwardly extending arms 20. Friction pads 22 are secured to opposite sides of the outermost portions of the arms 20. Plate 18 is located in the axial space provided bet~een outer covers 14.
As is well known, hub 12 is splined to a transmission 25 input shaft (not shown) and the friction pzds 22 are positioned between an axially movable clutch pressure plate and ar. axially stationary engine driven flywheel (not sho~n). Thus, cisc assembly 10 i$ free to move axially on the transmissior. n?ut shaft a limited distance but will always rotate with it.
It is essential that the damper unit not only establish the ariving connection between the rotzry clutch elemen.s, but also absorb the torque of the engine, thereby eliminatinc cha'ter and rattle in the vehicle power line. The preferrec e~oaiment incluaes resilient means comprising a first coil sprinc 24 ana a 35 second coil spring 26 coaxially disposea ~ithin the firs- coil spring 24. The resilient means consists of a plurality of circ~ ferentially spaced sprina sets adaptea to operate on the ~39Z49 sam~ circumferential axis. Covers 14 and 18 and have 21isned openings 14a and 18a for receiving and retaining and positioning the c02xizl spring sets to transmit a resilient drive bet~een the covers 14 and plate 18. While eight spring sets are silown, any 5 desired number can be used.
In the preferred embodiment, secondary or auxiliary cover members are provided primarily to serve 2S drive means for the inner springs 26. However, due to their location, the auxiliary cover members also provide aaditional and improved 10 drive surface area for outer springs 29, as will later be expl2ined in more detail. The secondary or auxiliary cover members comprise a pair of flat annular plates 28 located on opp~site sides of the hub flange 16 ana inside the outer or main covers 14. Rivets 30 extend through holes in the main and 15 auxiliary covers 14 and 28 and hub flange 16 to secure the parts together as a unitary structure. Auxiliary covers 28 are formed with stamped openings 28a for alignment with main cover openings 14a znd support plate openings 18a.
A plurality of flat, annular reinforcing plates 34 are 20 positioned on one side of support plate 18 to substantially fill the axial space between the auxiliary covers 28. A series of rivets 36 securely fasten the reinforcing plates 34 to supporting plate 18 so that they operate as a unit. Openings 34a identical to and aligned with s~pport plate openings 18a are formed in 25 reinforcing plates 34 .
From the description thus far, it will be evident that hub 12 and inner and outer covers 14 and 28, respectively, are secured together and will operate as the rotatable driven member of clutch disc assembly 10. The rotatable drive member of the 30 clutch disc assembly 10 consists of support and reinforcing plates 18 and 34 respectively, described above.
In addition to the resilient drive connection provided by coaxial springs 24 and 26, a positive drive connection is also proviaed between the rotary clutch elements. The resilient drive 35 is effective before the positive drive comes into play. This is accom~lished by a lost motion connection ~hich permits the coaxial springs 24 and 26 to f~nction prior to any direct drive 113g249 beins establishea between the rotary clutch elements. Referring to Figure 1, the lost motion is achieved through a plurality of outwardly directed teeth 40 on outer periphery hub flange 16 and a plurality of inwardly directed teeth 42 on the interior of support and reinforcing plates 18 and 34. The flange teeth 40 are normally maintained in a position ~id-way and eaually spaced from contact with the plate teeth 42. The spacing is aesigned to permit limited relative rotary movement between the hub 12 and plates 18 and 34 àuring which time the coaxial springs 24 and 26 10 function in their intended manner, i.e., abosrb or prevent minor transmission of shock loads and torsional vibration in the driveline and establish the initial resilient drive connection between the rotary clutch elements prior to positive drive engagement of teeth 40 and 42 As seen in Fig. 1, to accommoaate the limited rotation thct occurs between ~he hub 12 and plates 18 and 34, circumferentially elongated openings 44 are provided in covers 14 and 28 into which opposed heads of rivets 36 project. The openings 44 permit the necessary clearance for the rivet heads as the coaxial springs 24 and 26 are being compressed to establish the resilient driving connection or to absorb shocks and vibrations in the vehicle drive system.
Referring specifically to the resilient drive connection, the axially aligned openings in the outer and inner ~5 covers 14 and 28 and plates 18 and 34 are symmetrically and circumferentially spaced aajacent the hub flange periphery.
Outer cover openings 14a, in addition to being similar in shape to inner cover openings 28a, also include short inwardly directed arcuate lips 46 extending toward each other. 1ips 46 closely conform to the outer diameter of outer springs 24 and serve to retain the coaxial spring sets within the aligned openings.
As illustrated best in Figure 5, both springs 24 and 26 operate on the same axis and are positioned to be driven by thrust receiving surfaces of outer and inner cover opening side walls 14b and 28b, respectively. Because of the cover and spring locations, the circumferentially spaced ena walls 14b and 28b of both covers 14 and 28 are in constant contact ~ith both inner and 1~39249 outer springs 24 and 26. However, aue to the reduced diameter of inner spring 26, the spaced end walls 28b of inner cover openings 28a only are in driving contact with the inner spring enas.
A definite advantage exists in providing a secondary 5 cover in a coaxial d2mper spring arrangement s~ch as cisclosed.
Not only does the auxiliary cover provice an ideally located flat drive surface area, i.e., side walls 28b, for the inner spring ends, but it further creates additional driving surface area for the outer spring ends.
Axial space is of utmost importance and is very limited in heavy duty vehicle clutches. It is cifficult to provide greater drive area for the springs merely by increasing the thickness of the main covers because, in most applications, the length of the clutch assembly is specifically defined by the 15 vehicle manufacturer and cannot be easily changed. Because higher loading is being imposed on present damper springs by higher torque rise engines, means other thzn increased cover thickness must be provided so that increased stresses will not be developed at critical points, i.e., opening end walls ~nd spring 20 ends. This could result in da~lage to the part and pre~ature clutch failure.
Further, manufacturing procedures are such th2t when constructing outer cover openings, it is practically i~?ossible to form a perfectly square or flat end wall for drivinc contact 25 with the outer spring ends. It is known that the greater crive area provided for the spring ends, the better the load distribution and therefore the greater the torque capacity of the system. The actual thrust receiving surface or drive area presented in this instance is most clearly shown in Fis. 6 and 30 consists of substantially half-moon sha?ed portions incicated by rererence numerals 14b. In the present cc2xi21 spring arrangement, the drive surface area that would be made avcilable for engaging and driving tne outer s?rins ends is not the most satisfactory condition. This condition is improved by ?ut.ina 35 the thin auxiliary covers 28 inside the main covers 14. In this arrangement, the auxiliary covers 28 are p~sitioned so tha~ the end walls 28b, as seen in Fig. 5, are alisned with the coil ~L139249 portion OL the smaller inner spring 26. Thus the plate thickness of the 2uxiliary covers 26 is constructed and located to intersect the smaller inner spring 2~ across subst2ntially the entire aiameter of the end coil portions of the springs 26, 5 thereby providing an ideal s~are engaging surface for the inner spring ends. An additional benefit to this construction is that the eng2aing and drive surface inner cover opening ena walls 28b are iocated in a position to engage and thereby create a second contact or drive point for the ends of outer springs 24, thereby 10 producing more drive area for the outer springs.
The present invention provides a t~o-stage operation for coaxially arranged damper springs 24 and 26 in which varied d~rmping characteristics are afforded to meet requirements especially suited for use in vehicles equipped with high torque 15 enaines. The requirements are that a soft or weak initial char2cteristic be built into the clutch for cushioning clutch chatter, shock and vibration, and a hard or stiff rate be present at high loads for accommodating peak sho~k torques and transmitting high loads.
In the preferred embodiment, means are provided in plate openings 18a and 34a for engaging inner springs 26 to accomplish the desired two-staye operation. The side wall engaging means comprise inwardly directed projections 18c and 3~c formed on circu~.ferentially spaced thrust receivin.g side walls 18b and 34b 25 of plates 18 and 34. Projections 18c and 34c are located midway on side walls 18b and 34b and as a result produce a pair of tnrust receiving surfaces on each side wall 18b and 34b which are spacec on opposite radial sides of projections 18c and 34c. Thus projections 18c and 34c extend a short distance inwardly from siae walls 18b and 34b thereby defining adjacent cutouts on opposite sides of the projections 18c and 34c. The cutout portions are adapted to be aligned with the coil sect.ions of outer springs 24 but normally spacea a predeter~lined aistance from the springs ends in the neutral or inactive position of the - -lutch disc 10. The circ~mferential displacement or spacing of -he thrust surfaces on walls 18b and 34b relative to the thrust .:~faces on projections 18c and 34c is selected to achieve any ~13924~

oesireo amount of limited relative rotary movement that is reauired between the covers 14 and 28 and plates 18 and 34 for the first operating stage.
From the description thus far, it is apparent t:~zt 5plates 18 and 34 provide openings 18a and 34a with SiQe walls 18b and 34b having primary and secondary thrust surfaces designed to achieve the desired two-stage operation. These thrust surfaces, i.e., end walls 18b and 34b and projections 18c and 34c, can ezsily be altered to vary the load conditions to meet any number Oof steps or load requirements. For example, alternate or other selected openings in the plates 18 and 34 can be constructed similar to cover openings 28b (without projections 18c znc 34c) so that the load verses deflection curve in the disc assembly 10 will change in the first operating stage. Thus, any a~ount of 15 thrust surfaces can be provided to come up with various àegrees or steps in load in the first operating stage. It should also be noted that in any of these adaptations all the springs 2re still in a slightly prestressed condition within their respective openings. It is also known that the openings must be selected to 20 maintain the disc assembly 10 in a balanced condition.
By way of example and best illustrated in Figures 8 and 9, projections 18c and 34c and end walls 18b and 34b are designed so that only inner springs 26 will function as plates 18 and 34 rotate relative to covers 14 and 28 through an angle "a" in

2~ opposite directions from the neutral position shown in ~ig. 7.
The angle "a" is equivalent to 130' of relative travel. As plates 18 and 34 move through angle "a", to the right illustrated in Fig. 8, the projections 18c and 34c move a distance "x~, relative to covers 14 and 28, to the right in Fig. 9. During 30 this movement inner springs 26 are exercised and will be co..pressed between thrust surfaces on projections 18c and 34c and opposite thrust surfaces on inner cover openings 28b cnc outer spring ends move freely into the cutout portions on o~?osite sices thereof. If additional torque is a?plied and relctive 35 rotary movement exceeds the angle "a" in either direction, the second stage comes into play as the outer springs 24 a.e ?icked U2 bv plate side walls 18b and 34b and both springs 2' 2nd 26 are no~ in a position to operate in parallel to carrv loac.

~ s previously indicated, the lensths of bo.h sp~ings are substanti211y equal and selected so that in their inac.ive or free state, they are in a slightly prestressed conditicn. The outer springs 24 are prestressed between the thrust receiving 5 surfaces on cover end walls 14b and 28b and inner s?rings 26 between thrust receiving surfaces of plate projections 18c and 34c. Further, it will be noted that in this inactive state, as seen in Fig. 7, the opposed thrust receiving surfaces of cover siae walls 14b and 28b and projections 18c and 3Gc are aligned 10 and therefore spaced apart an equal distance. Since these are the engaging surfaces for the spring ends, both springs norm211y have their end portions aligned in the same plane. The distance between the thrust receiving surfaces of projections l&c and 34c anc adjacent side walls 18b and 34b determine the amount of 15 torsional play that will exist in the first torsional rance.
Accordingly, thrust surfaces of side walls 18b and 34b are spzced apart greater distance than the thrust surfaces of proJections 18c and 34c in order to accomplish the desired result.
Illustrated in Fig~ 10 is a torque vs. deflec.ion graph 20 depicting rigid disc which has no compression springs, a conventional 3 coaxial damper disc ana the two-stage camper disc 10 of the present invention with various load modifications in the first stage. The various load conditions are acco~?lished by altering the number of plate openings 18a an~ 34a p~ovided 25 with projections 18c and 34c. In example No. 1, all eisht plate openings 18a and 34a have projections. In No. 2, only four plate openings have ~rojections. Example No. 2 has no projections with friction or hysteresis between the covers 28 and acjacent plates 18 and 34. In No. 4, all eight plate openings 18a and 3~a were 30 constructed without projections, i.e., identical to cover openings 28a ~ rom the foregoing, it will be app2rent that 'he present invention has provided a two-s.age coaxial spring camper that can easily be adapted to vary the rates of deflection be.~_en rotary 35 clutch elements. A further advantage is that the p.esent invention provides a two-stage damper which req~ires no additional space and therefore can be easily incorpora.ed in an existing clutch for a worn or damaged disc. Additionally, the two-s.2ge operation could be accomplished by resilient means in t~e form of one or more solid or tubular sleeve members and/or selecting members of greater or lesser stiffness to change the 5 torque capacity of the clutch.
~ aving thus described a preferred embodiment of the invention, it should be understood that the inver,tion is not to be limitea to the specific construction and arrangement - described. It will be apparent to those skilled in the art that 10 modifications or alterations may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A torque transmitting device comprising, a hub;
a cover secured to said hub, said cover defining at least one opening having spaced side walls;
a plate mounted on said hub for limited rotation relative to said hub and said cover, said plate defining at least one opening having spaced side walls, said plate opening adapted for alignment with said cover opening;
resilient means disposed in said aligned openings adapted to transmit a yieldable drive between said hub and said plate, said resilient means comprising a first resilient member and a second resilient member disposed in said first resilient member, each of said resilient members having end portions;
means on at least one of said plate or cover opening side walls for engaging one of said resilient members, at least one end portion of one of said resilient members spaced from said plate or cover opening side wall engaging means and engageable therewith upon limited relative rotation between said plate and said cover, and at least one end portion of the other of said resilient members engaging said plate or cover opening side wall engaging means.

2. A torque transmitting device according to Claim 1 wherein said side wall engaging means includes an inwardly directed projection.

3. A torque transmitting device according to Claim 2 wherein said side wall engaging means includes a second inwardly directed projection, and wherein said inwardly directed projections have spaced thrust surfaces, said spaced thrust surfaces and said cover opening side walls spaced apart an equal distance.

4. A torque transmitting device according to Claim 3 wherein said plate opening side walls include thrust surfaces spaced apart a distance greater than the distance between said projection sidewall thrust surfaces and cover opening sidewalls.

5. A torque transmitting device according to either one of Claims 3 and 4 wherein said resilient members are coil springs having equal lengths.

6. A torque transmitting device according to either one of Claims 3 and 4 wherein said resilient members are coil springs having equal lengths, said outer coil spring being held in tension between said cover side walls, and said inner coil spring being held in tension between said projection thrust surfaces.

7. A torque transmitting device according to either one of Claims 3 and 4 wherein said resilient members are coil springs having equal lengths, and said plate opening side walls are normally spaced from engagement with said outer coil spring end portions.

8. A torque transmitting device according to either one of Claims 3 and 4 wherein said resilient members are coil springs having equal lengths, said outer coil spring being held in tension between said cover side walls, said inner coil spring beind held in tension between said projection thrust surfaces, and said plate opening side walls being normally spaced from engagement with said outer coil spring end portions.